Operas aren’t meant to make sense. That’s why they sing them in languages you probably never learned. If they sang them in English you’d be angry rather than baffled. Plus all opera companies have, for some reason, too many costumes and are thus always looking to fast-track operas with scope for costume changes and extensive cross-dressing. It also explains why there’s always an aria in which a moustache-twirling, straight Lothario questions his sexuality after falling for a new lad in uniform and why, for plot reasons that make no sense, he has to go undercover as a milkmaid in act two, even though the bloke who plays him weighs 120kg and was once a prop forward for Llanelli Rugby Football Club.

No wonder, in such circumstances, that a Times classical music critic confessed earlier this year to still not understanding the plot of Mozart’s Marriage of Figaro. To help him, and perhaps you, understand the incomprehensible, here are some opera synopses simplified, with a festive nod towards Giodarno’s Andrea Chénier – because the BBC is going to be showing David McVicar’s Covent Garden production on Friday 18 December. The last thing I want this festive season is for Guardian readers to settle down to watch tenor Jonas Kaufmann sing the title role, stupidly mystified by the story. First, let’s help out that Times writer.

Mozart’s The Marriage of Figaro (1786)

Gerald Finley as Count Almaviva and Camilla Tilling as Susanna in Le Nozze Di Figaro by Mozart at the Royal Opera House. Photograph: Tristram Kenton for the Guardian

Figaro is understandably furious to learn that his master Count Almaviva is trying to put the moves on his fiancée Susanna. Almaviva cites precedent: it’s his feudal droit du seigneur to sleep with a servant girl on her wedding night before her husband – even to me, that sounds dubious. So, Figaro comes up with a cunning plan. He gets Susanna to write to the count agreeing to a tryst, but plans to send in Susanna’s stead a page, Cherubino, dressed in women’s clothing for what promises to be an evening of old-school sexual harassment. The count’s long-suffering wife is in on the deceit, hoping (insanely in my view) that if he’s exposed thereby as a philandering sex pest he might cease and desist with the extra-marital groping. She’s not the brightest bulb in the palace.

The plan goes wrong when the count stumbles into the room while Cherubino is getting into his disguise

The plan goes wrong when the count stumbles into the room while Cherubino is getting into his disguise. Just in time, the randy page dives into a closet or under some antimacassar or another convenient hiding place. Just as well: the count is on the warpath over Cherubino having the temerity to fancy the countess, and the fact that the page is now unaccountably wearing women’s clothes would hardly be used as exculpatory evidence if he could be found.

Worse yet for Figaro, an elderly lady called Marcellina pops up with her lawyer Bartolo claiming that Figaro agreed to marry her if he failed to repay a debt. He hasn’t repaid so Marcellina demands what’s hers. Happily her plan is scuppered by the big reveal: Figaro is Marcellina’s son and so, even in the morally freewheeling 18th century, can no longer become her spouse. Figaro turns out to have been Marcellina and Bartolo’s love child, abandoned when he was slightly more than a twinkle in the lawyer’s eyes. So Figaro and Susanna can get married after all. Yay! Marcellina and Bartolo decide they’ll get hitched at the same time, this being near the opera’s big finish and all.

But the count still has designs on Susanna and arranges to meet her for a feudally justified grope-fest. As before, someone will stand in for Susanna. But who? In the end, it’s the countess who turns up at the trysting spot in the servant girl’s outfit, having lured the Count thither with a letter containing Susanna’s trademark pin (don’t ask). Mid-fondle the countess reveals her true identity and the count realises his lover is his wife. She forgives him, which is more than I would have. All the foregoing has to be understood in the context of its setting just before the French Revolution when, did they but know it, toffs like Count Almaviva quite understandably got their comeuppance.

Giordano’s Andrea Chénier (1896)

Jonas Kaufmann as Andrea Chenier at the Royal Opera House. Photograph: Tristram Kenton for the Guardian

It’s 1789 in the palace of the Countess of Coigny. The toffs arriving for the ball don’t have the hindsight necessary to recognise the historical significance of that date and that they, like their coevals in the Marriage of Figaro, are about to be strung up by their own entrails.

Some poor people press their noses against the windows begging for crusts, or preferably something from the cheese plate

Among the guests is the eponymous romantic poet, who fancies the countess’s daughter Maddalena. Unfortunately so does the servant Carlo Gérard. The rivals have one thing in common: they’re talking about a revolution. In fact, when Andrea improvises a frankly terrible poem about the suffering of the poor, Maddalena has to apologise to the guests, who continue to dance the gavotte even when some poor people press their noses against the palace windows begging for crusts – or preferably something from the cheese trolley and a few glasses of Pouligny-Montrachet. Scandalised at this callous indifference to the cheese-and-wine demands of the downtrodden, Gérard resigns from service and commits himself to the downfall of the upper classes.

Act two and the world has turned upside down. Maddalena goes by the name Speranza after losing her palace in the revolution, and wears a fetching hood to conceal her identity as aristo scum. Meanwhile, her former servant girl Bersi has become a merveilleuse(one of the foppish ladies in the time of the French Directory) and Gérard has become a leading functionary of revolutionary nut job Robespierre. Andrea, meanwhile, has been advised to biff off abroad on a false passport, but instead moons about in cafes, singing and attracting the attention of Robespierre’s spies and the mysterious hooded Speranza.

She reveals her identity to the poet and, overcome with mutual ardour, they sing a passionate duet, thus attracting Gérard who starts a fight with Andrea in which he is wounded and, believing he is dying, warns the poet that he should flee the wrath of guillotine-loving prosecutor Fouquier-Tinville. But will our love-devoted poet flee and thus risk losing his beloved Maddalena? Oh, have a guess.

Instead, Andrea is arrested and Gérard draws up false charges for the poet’s trial. The arrest, you see, is a pretext to get Maddalena to turn up at Andrea’s trial and declare her identity in the hope of saving the dashing poet she adores. When Maddalena appears, Gérard forces himself upon her and she declares she will surrender her virtue if her beloved Andrea is released. Overcome, you’d hope, with self-loathing, Gérard realises: a) Maddalena loves not him but Andrea, b) he’s become a git corrupted by revolutionary power and, c) that he can’t in all conscience fit up the poet on false charges.

But when Gérard admits the false indictment to Fouquier-Tinville, the latter continues with the prosecution and soon our hero is in jail awaiting execution. Happily, Maddalena joins him there, having bribed a jailer so she can switch places with a convicted noblewoman.

As day dawns, Andrea and Maddalena are led off, possibly in a tumbril, to face the revolutionary injustice of Madame La Guillotine, in a kind of grisly post-Wagnerian liebestod sung in McVicar’s production by Jonas Kaufmann and Eva-Maria Westbroek. If you aren’t sobbing on to your remote control at this point, there’s something wrong with you.

Verdi’s Ernani (1844)

It’s 1519 in Aragon. Elvira is a noble Spanish lady betrothed to ageing grandee Don Gomez de Silva but has the hots for the bandit Ernani who, you’ve guessed it, isn’t all he seems. As if that weren’t complicated enough, Spanish king Don Carlos fancies Elvira and to further his suit dresses as a peasant and tries to abduct her, only to be confronted by Ernani.

I haven’t yet seen an Elvira mouth “Yeah, whatever” and roll her eyes heavenwards at this advice but I’d like to.

Silva arrives and challenges both Carlos and Ernani to a duel before recognising the king and falling to his knees. Thus is established the prevailing dynamic: three dudes after one woman who doesn’t get a say in which, if any of them, she’d like to spend the rest of 1519 canoodling with. In one key scene, Silva spares Ernani, who in gratitude gives him a hunting horn and tells him that whenever he wants him to kill himself he just has to blow on the horn. Silly, yes, but plot-wise, crucial.

Later, Ernani reveals himself to the king: he’s not a badass bandit but Don Juan of Aragon whose lands the monarch appropriated. The king, overcome with remorse, agrees that the man he wronged should marry Elvira. And they do. But it’s not over yet.

In act four, Ernani, now with Elivira, hears a bugle call, heralding the arrival of Silva with a dagger with which Ernani, all-too-obligingly, stabs himself to death. But even as he expires, he manages to sing a trio with Silva and Elvira, before advising Elvira that she must go on living. I haven’t yet seen an Elvira mouth the words “Yeah, whatever,” and roll her eyes heavenwards at this advice but I’d like to.

Wagner’s Parsifal (1882)

Iain Paterson as Amfortas and Andrew Greenan as Titurel in English National Opera’s production of Parsifal. Photograph: Tristram Kenton for the Guardian

Amfortas, the Grail king, has a horrible suppurating wound, poor chap, and yearns for death. Wagner’s conceit here is that the wound can’t be healed with proper medicine but only by an enlightened fool with a mystic spear, which explains why he never became a GP. Enter the opera’s eponymous spear-wielding chump, preceded on to the stage by the clump of the dead swan he’s just shot.

Later, in the enchanted garden of magician Klingsor’s castle, flower maidens attempt to ensnare Parsifal with a leotarded music-and-movement routine borrowed from early Kate Bush, but he doesn’t swing that way. Instead he confronts Klingsor who hurls the sacred spear at Parsifal but it only hovers above the latter’s head. Parsifal then makes the sign of the Cross – at which point Klingsor’s castle collapses – before seizing the spear and baptising Kundry, thus ending her curse. Parsifal next heals Amfortas’ wound with the spear, then grasps the Holy Grail the Grail knights have been guarding. It starts to glow like something out of early Star Trek. While knights and chorus sing “Miracle of supreme salvation! Our Redeemer redeemed!”, the penitent Kundry sinks lifeless at the altar, absolved of her sins, which not only seems sexist and wrong but, like much else in the plot, random.

Mozart’s The Magic Flute (1791)

It doesn’t seem to have occurred to him that the bird outfit might explain his lack of success with the ladies.

In a distant land, Prince Tamino is attacked by a big serpent but saved by three ladies who are servants for the Queen of the Night. They show him a picture of her daughter Pamina – with whom he falls in love – and who, Tamino discovers, is held prisoner by magician Sarastro. Given a magic flute by the Queen’s ladies, he heads off to rescue his near-namesake and make her his, accompanied by Papageno, a bird-catcher dressed in a bird-like outfit who arms himself with some bells for the forthcoming ordeal. Papageno sings his complaint: he doesn’t have wife nor girlfriend. It doesn’t seem to have occurred to him that the bird outfit might explain his lack of success with the ladies.

At Sarastro’s bombastic, Grand Designs-reject lair, Tamino endures three themed tests – silence, water and fire – in order to win his unseen lover. It’s like Total Wipeout in fancy dress. Papageno is also offered a girlfriend by Sarastro if only he can pass his tests. He can’t pass these tests, but through the power of his magic bells, still gets to meet and fall in love with his near-namesake Papagena who, conveniently, is also into birds.

Yvonne Howard, Lee Bissett, Susanna Tudor-Thomas and Toby Spence as Tamino in The Magic Flute at English National Opera. Photograph: Tristram Kenton for the Guardian

But it’s not all billing and cooing for the four lovers. Pamina’s mother, the Queen of the Night is furious. She tries to break into the temple of Sarastro, but is hit by a thunderbolt, and goes to hell, like the butt of a Les Dawson mother-in-law joke. Which is obviously sexist and unfair but also serves as an allegory of the (serious face) modern-day perils of helicopter parenting.